It is well-known that plasma's can be used to treat a surface; with the use of a plasma, it is possible to etch, to deposit a material onto a substrate, and/or to change a property of a surface of a substrate, e.g. changing it from hydrophobic to hydrophilic and chemical attachment of atoms. The latter can for example be used in the process of metalizing a plastic substrate (see for example M. Charbonnier et al. in Journal of Applied Electrochemistry 31, 57 (2001)). In this process, a plasma makes the surface of a plastic suitable for attachment of Palladium, on which a metal layer can be grown. Compared to many other metalizing methods, this method has the advantage that the temperature can remain low, which is necessary for plastics having low melting points. For the production of plastic electronics like RFID tags and OLEDs, plasma treatment may thus be useful.
For these applications, making patterned structures directly with the plasma on the surface reduces the number of steps for the fabrication of the electronics. Further, compared to traditional mask/etch methods, there is no waste of metal (due to deposition and subsequent etching of the metal layer), reducing environmental burden. Also for other applications, like labs on chips, direct patterning with a plasma would be useful.
Known devices for directly patterning a surface with a plasma are described in DE 10322696 and in Surface & Coatings Technology 200, 676 (2005). These devices use a mask provided with a desired pattern for generating that pattern. This may be a good method for mass production, but, as making a mask is quite expensive, takes time and must be performed each time a new pattern is required, a maskless method would be preferable for production of smaller amounts.
Another device for directly patterning a surface with a plasma is known from U.S. Pat. No. 4,911,075. This device utilizes a precisely positioned high voltage spark discharge electrode to create on the surface of a substrate an intense-heat spark zone as well as a corona zone in a circular region surrounding the spark zone. The discharge electrode is scanned across the surface while high voltage pulses having precisely controlled voltage and current profiles to produce precisely positioned and defined spark/corona discharges in register with a digital image. Although not using a physical mask, this device has the disadvantage that complicated precise control of the high voltage pulses is required. Further, since the device uses a counter electrode behind the substrate, only thin substrates may be used. Also, spark discharge may not be desirable for certain processes of deposition, etching and hydrophilation.
In PCT/NL2008/050555 a method and apparatus are described that relate to plasma patterning. PCT/NL2008/050555 describes a method and apparatus wherein the positioning means are arranged for positioning the first electrode selectively with respect to the second electrode. The first electrode can be positioned in a first position in which a distance between the first discharge portion and the second discharge portion is sufficiently small to support the plasma discharge at the high voltage difference, and in a second position in which the distance between the first discharge portion and the second discharge portion is sufficiently large to prevent plasma discharge at the high voltage difference.